What is the ratio of 21 hours to 2 days?

To find the ratio of 21 hours to 2 days, you first need to convert both time periods to the same unit. Since there are 24 hours in a day, 2 days is equal to 2 x 24 = 48 hours. Therefore, the ratio of 21 hours to 2 days is 21:48, which can be simplified to 7:16 by dividing both numbers by their greatest common factor, which is 3 in this case.